1. Field of the Invention
The present invention relates to a disposable container. More particularly, the present invention relates to a thermoplastic film, which is heat and pressure fused to the inner and/or outer surfaces of the sidewall of a thermoplastic container, and optionally, to the inner and/or outer surfaces of container's base. The container is generally pre-formed via a molding process from expandable thermoplastic particles, e.g. expandable polystyrene particles (EPS). The container is used for holding liquids, such as coffee or foods containing oil and/or fat components such as precooked fat-containing foods, e.g. instant noodles, soups, fried chicken, and the like.
2. Background Art
The manufacture of molded articles, such as containers, i.e. cups, bowls, etc. from expanded thermoplastic particles is well known. The most commonly used thermoplastic particles are expandable polystyrene particles known as EPS. Typically, polystyrene beads are impregnated with a blowing agent, which boils below the softening point of the polystyrene and causes the impregnated beads to expand when they are heated.
The formation of molded articles from impregnated polystyrene beads is generally done in two steps. First, the impregnated polystyrene beads are pre-expanded to a density of from about 2 to 12 pounds per cubic foot. Second, the pre-expanded beads are heated in a closed mold to further expand the pre-expanded beads to form a fused article having the shape of the mold.
The expandable polystyrene particles used to make foam containers are generally prepared by an aqueous suspension polymerization process, which results in beads that can be screened to relatively precise bead sizes. Typically, bead diameters are within the range of from about 0.008 to about 0.02 inch. Occasionally, cups are made from particles having bead diameters as high as 0.03 inches.
In spite of careful bead size control, one problem, which continues to plague the container industry, is that after a period of time the EPS containers have a tendency to leak coffee or the oil and/or fat components in food substances carried by the containers. That is, the coffee or the oil and/or fat permeate around the fused polystyrene beads onto the outer surface of the sidewall of the container. The result can be an unsightly stain on the outer surface of the sidewall of the container and/or inconvenience to the holder of the container.
Several approaches have evolved over the years directed toward the reduction of leakage in these containers for retaining liquids and/or pre-cooked foods.
Amberg et al., U.S. Pat. No. 4,036,675 discloses a container made from foamed plastic material, preferably foamed polystyrene, which is lined on one or both sides with unoriented polyolefin film, preferably polypropylene. The film is secured to the foamed plastic base material using as a heat-sensitive adhesive a vinylic polymer or polyamide resin. The film is coated with a wet adhesive and dried before laminating the film to the foam material. Laminating is done by heating the foam material to 250-275° F., preheating the coated film to 100-180° F., and pressing the coated film surface against the heated foam using a cold platen or roller for 10 to 15 seconds.
Sonnenberg U.S. Pat. Nos. 4,703,065 and 4,720,429 disclose thermoplastic polymer foam cups for retaining coffee that are molded from thermoplastic polymer particles whose surfaces are coated with a fluorosurfactant before molding.
Sonnenberg U.S. Pat. No. 4,785,022 discloses a method for enhancing the coffee retention of molded foam cups, which involves coating the expandable polystyrene particles with various rubber polymers and copolymers. The rubber useful in the invention can be selected from the group consisting of polybutene, polyisobutylene, isobutylene-butene copolymer and butene-ethylene copolymer.
Arch, et al. U.S. Pat. No. 4,798,749 approaches the problem of coffee leakage by replacing conventional blowing agents such as butanes, n-pentane, hexanes, and the halogenated hydrocarbons with isopentane in the expandable styrene polymer particles.
Ikeda, et al., U.S. Pat. No. 4,698,367 discloses expandable thermoplastic resin particles in which the thermoplastic resin in which a copolymer composed of a fluorinated vinyl polymer part and a hydrophilic vinyl polymer part covers or is included on the surface or in the surface layer of the expandable thermoplastic particle. These resin particles are useful for producing package containers for oily or fatty foods.
Sakoda et al., U.S. Pat. No. 6,277,491 B1 is directed to the prevention of oil from penetrating into a vessel obtained from expandable thermoplastic resin beads through molding. This is achieved by coating the surface of the resin beads or incorporating the resin beads with a fluorine-containing block copolymer comprising a fluorine-containing vinyl-type polymer segment derived from a fluorine-containing vinyl-type monomer and a lipophilic vinyl-type polymer segment derived from a lipophilic vinyl-type monomer.
The containers of the above prior art are generally addressed to polystyrene containers, such as cups or bowls. The following patents pertain to paper cups that are either spray coated or that contain a thermoplastic resin film either for heat insulating purposes or for producing a high impermeability to liquids.
For example, Suzuki et al., U.S. Pat. No. 4,206,249 discloses a process for producing a paper container having high impermeability to liquid which comprises spray coating a polymerizable solution containing a prepolymer onto a wall surface of a previously fabricated paper container and irradiating the coated wall with ultraviolet light to effect the setting of the prepolymer on the wall surface of the container. This forms a coating, which is impermeable to liquids, such as water, milk, soft drinks, oils, etc. This '249 patent also teaches in column 2, lines 45-62, that there is a lining method in which the interior wall surface of the container is lined with a thermoplastic film. The thermoplastic film is first laminated onto a blank and the blank is formed into a container.
Iioka, U.S. Pat. No. 4,435,344 discloses a heat-insulating paper container where the outer and inner surfaces of the body member are extrusion coated or laminated with a thermoplastic synthetic resin film. The resin film is converted into a foamed layer on the paper substrate and then the container is formed. The result is a container with good thermo-insulation properties. This film preferably is polyethylene but as taught in column 3, lines 50 -55, this resin film can be polypropylene, polyvinyl chloride, polystyrene, polyester, nylon and the like.
Iioka et al., U.S. Pat. No. 5,490,631 discloses a heat insulating paper container comprising a body member wherein a thick foamed heat insulating layer is made of a thermoplastic synthetic resin film is formed in the printed area of the outer surface and a less thick foamed heat-insulating layer that can be made of the same thermoplastic synthetic resin film is formed in the non-printed area of the outer surface. The thermoplastic synthetic resin film is typically polyethylene.
Breining, et al., U.S. Pat. No. 6,416,829 B2 discloses a heat insulating paper cup where the body member is coated on its outside surface with a foamed low density polyethylene, and on its inside surface with an unfoamed modified low density polyethylene.
None of the containers of the prior art have a thin thermoplastic film fused to the inner and/or outer surfaces of a foam molded container for retaining food items such as coffee, soups, meats, and the like for the purpose of reducing the penetration of the liquid and/or the oil or fatty components in these food items through the foam container.